Generally, fiber structures of the kind used for cushioning and packaging (for example, pulp packaging, peanuts, egg crates and the like) are formed from cellulose fibers using a wet forming process. The product is formed on a solid, rigid mold that is covered with a screen material on all of its surfaces. The strength of the resultant structure is due to entanglement of the fibers and hydrogen bonding. Some strength-enhancing chemical or resin may also be added.
The strength resulting from fiber entanglement depends upon the type and length of the fibers used. Bonding of cellulosic fibers depends on fiber-to-fiber contact, which is increased with increased compression of the fiber mat. Current industry use of compression of pulp-molded articles ranges from no compression to compression by mating male and female rigid molds that have close tolerances for higher consolidation of the fibers.
If the structure has any three-dimensional parts, the sides of the structure must have a draft angle, so that the compression force of the mating molds has a component force on the sides of the mold normal to the structure being formed. If the sides of the mold are substantially vertical, the mating part is not able to apply a compression force component normal to sides of the structure.
The structural performance of a pulp-molded article can be enhanced by fiber addition or by increased bonding. Increased bonding may allow for a reduction of fiber content for a given performance need. U.S. Pat. No. 4,702,870, issued to Setterholm et al. for a "Method and Apparatus for Forming Three Dimensional Structural Components from Wood Fiber" and U.S. Pat. No. 5,277,584, issued to Hunt for "Methods and Apparatus for Making Grids from Fibers" illustrate several methods and devices for forming products from the materials herein addressed.
It is an object of the invention to provide a method and apparatus for making three-dimensional structures from fibers for various structural uses.
It is another object of the invention to provide a method and apparatus for making three-dimensional structures from fibers which utilizes compressive forces normal to the surfaces of the object being formed as a result of the composition of the mold.
It is still another object of the invention to provide a method and apparatus for molding three-dimensional objects from fibers which permits the fabrication of such objects in a wide variety of structural configurations.
It is still another object of the invention to provide a method and apparatus for manufacturing three-dimensional objects from fibers where the objects consist of a plurality of interconnected ribs without integral surfaces covering the ribs.
It is a further object of the invention to provide three-dimensional objects manufactured from fibers where the objects consist of a plurality of interconnected ribs without integral surfaces covering the ribs.
It is a still further object of the invention to provide a method and apparatus for making a three-dimensional object from fibers permitting the cost effective use of both cellulosic and non-cellulosic fibers to create such three-dimensional objects.